Minimum fuel flow control responsive to altitude and flight speed



May 16, 1961 H. SAVILLE ETAL 2 MINIMUM FUEL FLOW CONTROL RESPONSIVE TO ALTITUDE AND FLIGHT SPEED Filed Aug. 25, 1959 At mosph crlc Pressure A|r Intake Total Pressure 2 IIIIII r ""III'IIIJ'II. VIII III" II/ I Total Pressure Pressure 6 44 O 58 i J 66 4 0 67* 62 I B\\\\XY/ 7 7O O o O 54 1 O Atmos here 0 l 7b O 0 a v 52 -75 1 9 B M O -8I FIG 2 5| 7 3 All Intake Total Pressure IN ENTOR HA qLo JAVIL-LE Er lI-L BY Wan-14. y kw nited States atent Ofiice Patented May 16, 1961 Harold Seville and Robin M. Dakin, both Bristol Siddeley Engines Limited, Park Side, Coventry, England Filed Aug. 25, 1959, Ser. No. 836,014

Claims priority, application Great Britain Sept. 4, 1958 8 Claims. (Cl. 60-39.28)

The invention relates to a fuel system for a gas turbine engine.

An object of the invention is to provide a rising-idling device for an aircraft gas turbine engine by which the speed of the engine can be maintained above a varying minimum idling speed, below which it is impossible to maintain adequate combustion at given altitude and forward speed.

According to the invention, a fuel system for a gas turbine engine includes a device responsive to variations of air intake ram pressure and atmospheric pressure, and arranged to over-ride throttle control means of the engine to prevent the reduction of selected engine speed, by the throttle control means, below a minimum value required to maintain adequate combustion under theconditions to which the device is responsive, the device being inoperative until the air intake ram pressure has increased to a predetermined value, the atmospheric pressure has decreased to a predetermined value or the combined effect on the device of increased air intake ram pressure and decreased atmospheric pressure has reached a predetermined value.

Preferably, the device comprises a first pressure-responsive capsule responsive to variation of air intake total pressure compared with atmospheric pressure and thus to air intake ram pressure and a second pressure-responsive capsule responsive to atmospheric pressure, the first and second capsules being interconnected to form a capsule unit having an effective length dependent on the individual length of each capsule, the effective length determining the amount by which the device over-rides the throttle control means. The capsules may be arranged back-to-back in a stack, the said eifective length being the overall length of the stack. Alternatively the capsules may be arranged side-by-side and are interconnected at one end by a link pivotally connected to each capsule and at the other end by a link connected rigidly to each capsule, the said effective length being the distance between the mid-points of the links.

The capsule unit may be fixed at one end, the other end being movable in accordance with the expansion and contraction of the capsules and engaging a member of the throttle control means to limit the operation of the throttle control means in dependence of the said effective length, when a control lever of the throttle control means has been moved in the closing direction.

Instead of the capsule unit being fixed at one end, it may be so arranged that both ends are movable, one end of the capsule unit being arranged to engage a valvecontrolling member of the fuel system to apply a loading on the member in the valve-opening sense and the other end of the capsule being arranged to engage a movable stop operated by a control lever of the throttle control means, the arrangement being such that the loading on the said member can be applied only when the effective length of the capsule unit has increased to a predetermined length and when the control lever has been moved towards the closed position sufficiently for the stop to engage the said other end of the capsule unit. The stop may be in the form of a cam, of such profile that when the cam is in engagement with the said other end of the capsule unit, the valve-closing effect due to continued operation of the control lever towards the closed position is counter-acted by the valve-opening effect exerted by the capsule unit, when it is of the said predetermined length.

The fuel system may be either governor controlled or of the flow-control kind and where both ends of the capsule unit are movable, the capsule unit may be arranged either to apply a loading to a governor-operated valve controlling arm in opposition to the loading effected on the said arm by the governor, or to exert an opening load on a control valve of the flow control system, respectively,

By way of example three embodiments of the invention as applied to a gas turbine aircraft engine will now be described with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic sectional view of part of the fuel system of the first embodiment;

FigureZ is a similar view of the second embodiment; and

Figure 3 is a diagram showing a modification of part of Figure 1 or Figure 2.

In the first embodiment, shown in Figure 1, the risingidling device comprises a chamber 35 open to atmospheric pressure at 32 and containing a capsule unit consisting of two pressure-responsive capsules 31 and 33 positioned back-to-back. One of the capsules 33 is open to air intake total pressure at 34 and expands in response to the difference between air intake total pressure and atmospheric pressure and thus to air intake ram pressure. The other capsule 31 is evacuated and thus expands in response to atmospheric pressure (i.e., altitude). The combined effective length of the capsule unit therefore changes on variation of the air intake ram pressure or the atmospheric pressure or on variation of air intake ram pressure and atmospheric pressure together. The end of the capsule unit adjacent the capsule 33 is fixed and the other end carries a rod 36. On expansion or contraction of the capsule unit the rod 36 moves through a corresponding distance. The end of the rod 36, remote from the capsules 31, 33, is connected to a lever 30 pivoted at 37 to a wall of the chamber 35. The end of the lever 30 remote from the rod 36 is in the form of a stepped cam or ratchet. The surface of each'step of the cam or ratchet is normal to a radial line through the pivot 37.

The remainder of Figure 1 shows part of a governorcontrolled fuel system as described with reference to Figure 1 of co-pending application Serial No. 836,015, tiled August 25, 1959. Briefly, an engine-driven governor 9 has a shaft 8 which is arranged to bear axially, in accordance with rotational speed against an arm 7 carried on the end of a lever 4. The lever 4 carries a halfball valve 1 which controls the flow of fuel between two ducts 2 and 3. The arm, 7 is also acted upon by an adjustable spring device comprising two angularly adjustable springs 14 and 15. These springs are adjusted by means of pivotally mounted plates '20, 21 mounted for pivotal movement on a common shaft 22. The plates 20, 21 and the common shaft 22 are shown in laterally separated positions for convenience of illustration only. The

common shaft 22 is turned by a lever 23 attached to a.

throttle control lever, not shown. Angularly fast with the shaft 22, there is an arm 27 which is' attached by a link 28 to operate a pivoted pawl 29, mounted in the housing 35 of the rising-idling device.

. As the throttle control lever is moved towards the closed or idling positions, the pawl 29 is pivoted upwardly, in a clockwise direction, as viewed in Figure 1. Also, in certain conditions of atmospheric pressure, i.e., altitude and air intake total pressure, the effective length of the capsule unit 31, 33 is such that the cam lever 30 is pivoted so as to be engaged with the pawl 29. When the pawl 29 has engaged a tooth of the cam lever 30, no further closing movement by the throttle control lever can move the shaft 22; but the throttle lever can still be brought into contact with the stop 25 by overriding spring-loaded pawls 26. This prevents the pilot from over-stressing the throttle control linkage, although the shaft 22 has been arrested by the rising-idling device. Thus the load exerted on the arm 7, and hence governed speed, by the adjustable spring device is prevented from reduction below a value determined by the atmospheric presure, i.e., altitude, and air intake ram pressure, i.e., forward speed, detected by the rising-idling device capsules. The rising-idling device shown in Figure 1 thus ensures that a suflicient supply of fuel is maintained for adequate combustion under the conditions detected by the rising-idling device. The cam lever 36 may be mass balanced about the pivot 37 to reduce undesirable vibration effects.

In the second embodiment, shown in Figure 2, a chamber 62 contains a back-to back capsule unit 60, 61, similar to those of the first embodiment; but the capsule unit is not fixed to the wall of the chamber 62 at one end of the unit. In this embodiment the capsule 61 is responsive to air intake total pressure at 65 and the capsule 60 is evacuated and is responsive to atmospheric pressure, the chamber 62 being open to atmosphere at 63. The capsule unit 60, 61 carries, at the end thereof adjacent the capsule 61, a lever 66, which is pivoted in a bearing 67 mounted on a wall of the chamber 62 in a pressuretype pivot, sealed by an O-ring 68. The end of the lever 66, remote from the capsule unit 60, 61 engages a reversing link 69, pivoted to a rod 70, which applies a loading to a valve-controlling arm 43 in opposition to the loading applied to the arm 43 by the governor shaft 8 in accordance with engine speed. The other end of the capsule unit, i.e., the end adjacent the capsule 60 engages a cam 58 carried by a link 53 connected to the throttle control lever of the engine.

When the capsules 60, 61 have expanded to a total predetermined length, the cam 58 will be engaged by the capsule 60, provided that the throttle control lever has been moved sufficiently towards its idling position. A load will then be exerted on the valve-controlling arm 43 in response to pressure changes detected by the capsule unit 60, 61 or in response to further closing movement of the throttle control lever. The throttle control lever is arranged to operate a pivotally-adjustable spring 49 as described with reference to Figure 2 of co-pending application Serial No. 836,015, filed August 25, 1959. Briefly, the link 53 is connected by links 52 and 5 1 to a pivoted slotted plate 55. Movement of the plate 55 causes the spring 49 to be angularly adjusted, by means of the linkage 54, so that the load applied on the arm 43 can be varied via a curved pivotally mounted arm 48. The arm 48 is pivoted at 50. A spring 56 which can be manually pre-set also acts on the arm 48. The arm 43 is pivotally mounted in a fixed bearing 44, containing an O ring seal 45, and controls a half-ball valve 40, carried on the end thereof remote from the governor shaft 8 and the springs 49 and 56. The half-ball valve controls the flow of fuel to the engine between ducts 41, 42.

The capsules 60, 61 are so adjusted that there is just continuous engagement between the cam 58 and the valve controlling arm 43, under certain conditions, e.g., sea-level static idling conditions. When the effective length of the capsule unit 60, 61 is not suificiently long for there to be continuous engagement between the cam 58 and the valve-controlling arm 43 and/or when the throttle control lever has not been moved sufficiently to the closed or idling positions, the capsule unit 60, 61 is unable to exert any loading on the valve-controlling arm 43. The profile of the cam 58 is such that when the effective length of the capsule unit 60, 61 is such that there is engagement, through the capsule unit, between the cam 58 and the arm 43, reduction of load, on the arm 43, exerted by the springs 49 and 56 is compensated by a substantially equivalent increase in the lead, on the arm 43, exerted by the rising-idling device, by compression through the cam 58, as the throttle control lever is moved towards the closed position. By this embodiment of the invention, the extent, to which the throttle control means can oppose the governor force, is dictated by the forward speed and/or altitude; thus a sufficient supply of fuel is maintained for adequate combustion under those conditions.

Although the embodiments shown in Figures 1 and 2 relate to a governor-controlled fuel system, the risingidling device may instead act on a valve of a flow control system. For example, referring to Figure 2 the arm 43 may be arranged to move a diaphragm, responsive to the pressure difference across a restrictor in a fuel supply pipe to the engine, the diaphragm being arranged to open or close a valve controlling the flow of fuel through the said supply pipe.

In Figures 1 and 2, the capsules have been illustrated in back-to-back positions. They can alternatively be arranged side-by-side. Figure 3 shows diagrammatically a suitable alternative arrangement, which can be used in Figure 1, where one end of the capsule unit is fixed. Referring to Figure 3, the chamber 75 containing the capsules is open to atmosphere at 76. The evacuated capsule 77 is rigidly connected to the other capsule 78 which is open to air intake total pressure at 79. The rigid connection between the capsules is indicated diagrammatically by a plate 80, which is fixed to the chamber 76 at 81. The ends of the capsules opposite to the plate 80 are pivotally connected to a link 82, which is pivotally connected to an axially movable rod 83, which is equivalent to the rod 36 in Figure 1. The effective length of the capsule unit in Figure 3 is the distance between the mid-points of the link 82 and the plate 80. Where the device shown in Figure 3 is to be used in the arrangement shown in Figure 2, the plate 80 is not fixed at 81; instead the part 81 is arranged to be movable in a direction parallel with the axes of the capsules, so that it can engage the cam 58.

What we claim as our invention and desire to secure by Letters Patent of the United States is:

1. A fuel system, for an aircraft gas turbine engine, including a pressure responsive device, responsive to variations of air intake ram pressure and atmospheric pressure, a first stop movable by said device, pilotoperable throttle control means, a second stop movable on operation of said throttle control means, said first and second stops being movable into engagement with one another; but being normally spaced apart from each other, said engagement only occurring when said device has detected a limiting combined effect of increased air intake ram pressure and decreased atmospheric pressure and said throttle control means has been set below a minimum value required to maintain adequate combustion at the said limiting conditions detected by said device, said stops when engaged acting to over-ride the effect of setting said throttle control means below said minimum value.

2. A fuel system as claimed in claim 1 in which said device comprises a first pressure-responsive capsule, responsive to variation of air intake total pressure compared with atmospheric pressure and thus to air intake ram pressure, a second pressure-responsive capsule, responsive to atmospheric pressure, and means interconnecting said first and second capsules to form a capsule unit having an effective length dependent on the individual length of each capsule.

3. A fuel system as claimed in claim 2 in which the capsules are arranged back-to-back in a stack, the said effective length being the overall length of the stack.

4. A fuel system as claimed in claim 2 in which the capsules are arranged side-by-side and are interconnected at one end by a link pivotally connected to each capsule and at the other end by a link connected rigidly to each capsule, the said efiective length being the distance between the mid-points of the links.

5. A fuel system, for an aircraft gas turbine engine, including a pressure-responsive device, comprising a first pressure-responsive capsule, responsive to variation of air intake total pressure compared with atmospheric pres- I sure and thus to air intake ram pressure, a second pressure-responsive capsule, responsive to atmoshperic pressure, means interconnecting said first and second capsules to form a capsule unit, the capsule unit having an effective length dependent on the individual length of each capsule and being fixed at one end, and a pivotally mounted stepped ratchet-like cam carried on the other end of said capsule unit, the fuel system also including pilot-operable throttle control means and a pivotally mounted pawl connected to said throttle control means, said cam and said pawl being movable into engagement with one another; but being normally spaced apart from each other, said engagement only occurring when said capsule unit has detected a limiting combined eifect of increased air intake ram presure and decreased atmospheric pressure and said throttle control means has been set below a minimum value required to maintain adequate combustion at the said limiting conditions detected by said capsule unit, said cam and said pawl when engaged, coaeting to over-ride the effect of setting said throttle control means below said minimum value.

6. A fuel system, for an aircraft gas turbine engine, including a pressure-responsive device comprising a first pressure-responsive capsule, responsive to variation of air intake total pressure compared with atmospheric pressure and thus to air intake ram pressure, a second pressure-responsive capsule, responsive to atmospheric pressure, means interconnecting said first and second capsules to form a capsule unit, the capsule unit having an effective length dependent on the individual length of each capsule and each end thereof being movable, the fuel system also including pilot-operable throttle control means, a valve-controlling member, one end of the capsule unit being arranged to engage said valve-controlling member and the other end of the capsule contituting a first movable stop, and a second stop movable on operation of said throttle control means, said first and second stops being movable into engagement with one another; but being normally spaced apart from each other, said engagement only occurring when said capsule unit has detected a limiting combined effect of increased air intake ram pressure and decreased atmospheric pressure and said throttle control means has been set below a mum valve required to maintain adequate combustion at the said limiting conditions detected by said capsule unit, said stops when engaged transmitting loading from said throttle control means on to said valve-controlling member in the valve opening sense to over-ride the effect of setting said throttle control means below said minimum value.

7. A fuel system as claimed in claim 6 in which said second stop is in the form of a cam, of such profile that when the cam is in engagement with the said first stop, the valve-closing effect due to continued operation of the throttle control means towards the closed position is counter-acted by the valve-opening effect exerted by the capsule unit, when it is of the said predetermined length.

8. A fuel system as claimed in claim 6 in which the fuel system is of the governor-controlled kind, the capsule unit being arranged to apply a loading to a governoroperated valve-controlling arm in opposition to the loading effected on said arm by the governor.

References Cited in the file of this patent UNITED STATES PATENTS 2,422,808 Stokes June 24, 1947 2,633,830 McCourty et a1 Apr. 7, 1953 2,638,742 Carey May 19, 1953 2,715,311 Coar \Aug. 16, 1955 2,796,136 Mock Jan. 18, 1957 2,857,742 Deake Oct. 28, 1958 

